Elastic Network Interfaces

An elastic network interface (referred to as a network interface in
this documentation) is a virtual network interface that can include the following
attributes:

a primary private IPv4 address

one or more secondary private IPv4 addresses

one Elastic IP address per private IPv4 address

one public IPv4 address, which can be auto-assigned to the network interface for eth0
when you launch an instance

one or more IPv6 addresses

one or more security groups

a MAC address

a source/destination check flag

a description

You can create a network interface, attach it to an instance, detach it from an instance,
and attach it to another instance. A network interface's attributes follow it as it
is attached
or detached from an instance and reattached to another instance. When you move a network
interface from one instance to another, network traffic is redirected to the new
instance.

Each instance in your VPC has a default network interface (the primary network interface)
that is assigned a private IPv4 address from the IPv4 address range of your VPC. You
cannot
detach a primary network interface from an instance. You can create and attach an
additional
network interface to any instance in your VPC. The number of network interfaces you
can attach
varies by instance type. For more information, see IP Addresses Per Network Interface Per
Instance Type in the Amazon EC2 User Guide for Linux Instances.

Attaching multiple network interfaces to an instance is useful when you want to:

Create a management network.

Use network and security appliances in your VPC.

Create dual-homed instances with workloads/roles on distinct subnets.

Create a low-budget, high-availability solution.

For more information about network interfaces and instructions for working with them
using
the Amazon EC2 console, see Elastic Network
Interfaces in the Amazon EC2 User Guide for Linux Instances.

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